Unless otherwise indicated herein, the materials described in this section are not prior art to the claims and are not admitted to be prior art by inclusion in this section.
Cellular wireless networks typically include a number of base stations that radiate to define wireless coverage areas, such as cells and/or cell sectors, in which user equipment devices (UEs) (also referred to as wireless communication devices (WCDs)) such as cell phones, “smart” phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices, can operate. Each base station is coupled to network infrastructure that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) for voice communications and/or the Internet for voice and/or data communications for instance.
In general, a wireless network operates in accordance with a particular air interface protocol or radio access technology, with communications from the base stations to UEs defining a downlink or forward link and communications from the UEs to the base stations defining an uplink or reverse link. Examples of existing air interface protocols include, without limitation, Orthogonal Frequency Division Multiple Access (OFDMA (e.g., Long Term Evolution (LTE) or Wireless Interoperability for Microwave Access (WiMAX)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), and Global System for Mobile Communications (GSM), among others. Each protocol defines its own procedures for registration of UEs, initiation of communications, allocation of bandwidth for UE communications, handoff/handover between coverage areas, and functions related to air interface communication.
In practice, a base station may be configured to provide service to UEs on multiple carrier frequencies or “carriers.” Each carrier could be a time division duplex (TDD) carrier that defines a single frequency channel multiplexed over time between downlink and uplink use, or a frequency division duplex (FDD) carrier that defines two separate frequency channels, one for downlink communication and one for uplink communication. Each frequency channel of a carrier may then occupy a particular frequency bandwidth (e.g., 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, or 20 MHz) defining a range of frequency at a particular position (e.g., defined by a center frequency) in a radio frequency band (e.g., in the 800 MHz band, the 1.9 GHz band, or the 2.5 GHz band).
With this arrangement, a UE within the coverage area of the wireless network may engage in air interface communication with a base station. This arrangement enables UEs to communicate via the base station with various remote network entities or with other UEs served by the base station or by one or more other base stations.
In a number of markets, cellular wireless service is available from more than one service provider or “carrier,” each service provider deploying and operating its own wireless communication network, for example. Owing to unequal coverage of respective wireless communication networks of two or more different service providers, or other possible factors affecting relative coverage, a subscriber in one service provider's network may, from time to time, gain access to and receive service from the wireless communication network of a different service provider. When this occurs, the subscriber is said to be “roaming” in the different service provider's network. Customarily, the subscriber's network is referred to as the “home” network, and the “roamed-to” network is referred to as the “roaming network,” “visited network,” or “foreign network.” Service providers may typically establish “service level agreements” (“SLAs”) between each other to accommodate roaming of their respective subscribers in each other's networks. SLAs may specify how costs of providing un-subscribed service to each other's respective subscribers are identified, recovered, and resolved.